This invention relates in general to wireless communication systems, and more specifically to an apparatus for receiving and recovering frequency shift keyed symbols.
Digital wireless communication systems have utilized many different types of modulation for transmitting data. One type of modulation which has become popular is Gaussian frequency shift keyed (GFSK) modulation. The well-known Bluetooth wireless communication system, for example, utilizes two-level GFSK modulation.
A GFSK modulator performs filtering on the data symbols to be transmitted in order to limit the transmission bandwidth. This transmitter filter causes a significant amount of inter-symbol interference (ISI), making the symbols harder to detect in a receiver. In order not to exacerbate the ISI, prior-art GFSK receivers have generally utilized relatively wide-band selectivity filters, thereby reducing adjacent channel rejection. Additional elements, such as a post-detection filter (PDF) and a maximum likelihood sequence estimation (MLSE) element having four or sixteen states for a two-level GFSK channel, have been used to compensate for the ISI. The templates of the MLSE are generally used with a bandwidth matching that of the transmitter filter. Such additional elements add to the cost of the receiver and increase the total power consumption.
Thus, what is needed is an apparatus for receiving and recovering symbols transmitted in an FSK digital wireless channel. The apparatus preferably will achieve high sensitivity and adjacent channel rejection without requiring either the PDF or the four- or sixteen-state MLSE element.